Seasonal variation in plasma tryptophan in parturient women

• 1.

  1. Blood samples were collected from 71 subjects between thirty-six weeks gestation and six weeks postpartum. Sample collection was carried out over a ten-month period. Subjects entered the study in three phases, month of parturition being July-September, October-December, or January-April. Data from each group and each sampling point relative to parturition were analysed separately.

• 2.

  2. Seasonal variation in total tryptophan concentration was noted at six weeks postpartum, when women giving birth between January and April exhibited higher plasma levels than those in the other two groups.

• 3.

  3. Percent unbound tryptophan was highest in women giving birth between July and September, and lowest for the January to April group. This seasonal effect was highly significant from thirty-six weeks gestation to day two postpartum, had disappeared by day five postpartum and reappeared at six weeks postpartum. Plasma concentrations of unbound tryptophan changed in parallel with percent unbound tryptophan. There is some evidence for a partial dependence of plasma unbound tryptophan on environmental temperature.